This invention relates to new complexing agents suitable for complexing metal ions useful in pharmacological diagnosis, and to the resultant complexes and salts thereof and to the use thereof. Aminopolycarboxylic acids, their metal, complexes and metal complex salts and processes for their production are known: cf, for example, U.S. Pat. Nos. 2,407,645; 2,387,735; 3,061,628; 2,130,505 and 3,780,099; DE-OS 29 18 842 and DE-OS 31 29 906. The use of complexing agents or complexes or their salts in medicine has also been known for a long time. For example, complexing agents have been used as stabilizers of pharmaceutical preparations; complexes and their salts have been used as adjuvants for administering slightly soluble ions (e.g., iron); complexing agents and complexes (preferably calcium or zinc), optionally, as salts with inorganic and/or organic bases, have been used as antidotes to poisoning in the case of inadvertent incorporation of heavy metals or their radioactive isotopes; and complexing agents have been used as adjuvants in nuclear medicine during use of radioactive isotopes such as .sup.99m Tc for scintigraphy. Recently, paramagnetic complex salts were proposed as NMR diagnostic media in DE-OS 31 29 906. See the corresponding U.S. application Nos. 573,184 of Jan. 23, 1984 and its parent 401,594 of Jul. 26, 1982 as well as U.S. Pat. No. 4,719,098 of May 4, 1984, all of which disclosures are incorporated by reference herein.
All the complexing agents, complexes and their salts known so far cause problems when they are used clinically in regard to tolerance, selectivity of the intended bond and hence intended action and stability. These problems are the more pronounced the higher the molecular weight of the complexing agents, and the products derived from them must be dosed. For example, the insufficient renal tolerance of complexing agents available today and their tendency to bond ions essential for the organism, limit their use in metal poisoning therapy. The use, advantageous in itself, of heavy elements as constituents of X-ray contrast media to be administered parenterally has so far been thwarted by the insufficient tolerances of compounds of this type. For the paramagnetic, contrast-enhancing substances proposed so far for nuclear spin tomography, the differential between the effective and toxic doses in animal experiments is relatively narrow.
There is a need, therefore, for improvement for many purposes, above all, for better tolerated substances, but also for stable, easily soluble and sufficiently selective complexing agents, inter alia.